Streptococcus salivarius is a species of spherical, Gram-positive bacteria which colonize the mouth and upper respiratory tract of humans a few hours after birth, making further exposure to the bacteria harmless. The bacterium is an opportunistic pathogen which rarely makes its way into the bloodstream where it is associated with septicemia cases in people with neutropenia.
It has different characteristics when exposed to different environmental nutrients. In the lab a SYTA plate is used where it uses sucrose to produce a capsule around itself. On a GYC plate only glucose is available and thus S. salivarius is not able to make a capsule from glucose.